Radio receiving system



Jan. 26, 1932. las. F. MlEssNER 1,842,977

RADIo. REEIVING sYsTmr Filed July 20. 1929 Eltron/mi C Patented Jan. 25, 1932 UNiilEa armas reiterar essieu i BENJAMIN ,"E. MESSNER, 0F SHORT HILLS, NEW JERSEY, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO RADIO CORPORATION 0F AMERICA, OF NEW YORK, N.

OF DELAWARE Y Apgiieation' fiiea July 2o,

This invention relates to radio receiving systemsand particularly those employingk a number of stages of radio frequency amplifiers in cascade and energized by sources of fluctuating unidirectional current. l

In energizing a radio frequency amplier from Va source of fluctuatingpotential, such as a poorly filtered output of arectiier supplied from a cycle alternating current supplied byA mostcommercial generating plants of the present day, there results a modulation of signal currents received from a broadcasting station and amplified by suchan amplifier.

The problem of how such modulation can be obliterated Without distorting the signal currents is complex and therefore requires at least a brief summary of the variouslreactions occurring in a radio receiverV when energized from a source of fluctuating potential. g I

In a radio receiving system having one or more radio frequency amplifier stages, a de-` teetor, and one ormone audio frequency amplifier stages in cascade, or reflexed, when no signal is .being amplified by the radio fre quency stage, low frequency of the order of 60 cycles or harmonics thereof Will not be transferred to the detector through the radio frequency transformer. Therefore, the system in this condition must be neutralized Lfor hum components developed by the detector and audio stages of amplification.

Then a receiver, non-receptive of signals, is neutralized so that no hum is heard in the loud speaker and then a 'signalA vis tuned.A in,

it will be noted that there is an accompany# ing hum developedv`ralong with the audible. signals. This is especially true of a system in which the lilterV system has beenreduced to al point insufcient for the load placed thereon. V i y I have described in a ynumber of copending applications'methods by Which this hum accompanying the signal in the loud speaker may be eliminated by re-neutralizing--the system While operating during the reception of signals. j

VIn such systems I have found the objection that While'no signal is being received there Y., A CORPORATION RADIO RECEIVING sYsrFivr 1929. Serial No; 379,672.

is hum developed in the loud speaker, a feature objectionable to Vsome users thereof. However, theuprimary objection that I iind is that the modulation of the high frequency frequency tubes Within theVra-dio frequency t systems Without radio frequency regeneration being caused thereby. I v

'TWo modifications are shownin the accompanying drawings lin which like reference characters indicate corresponding parts throughout, insofar as possible.

Referring to the drawings VT designates a vacuum tube, the input circuit `of which includes the secondary 'Ii-S1 of a radio frequency transformer RT1, tunable by means of a variable condenser VC1. The primary RPI of the transformer RTl is so connected that it has flowing therein carrier currents modulated at audio frequency, for example as being included in an antenna circuit or constituting the output coil similar to BP2 of a preceding` radio frequency stage, the circuits of which are similar to those to be hereinafter described.

Y The output circuit of the tube VT includes the primary HP2 of a radio frequency transformer RT2, the secondary KS2 of which is tunable by means of a variable condenser V02.' The lament of the tube VT is heated from asource of alternating currentthrough a filament heating transformer I'IT, th'e'secondary HS of which is shunted by a center tap potentiometer"CT. A

Y In the circuit of Fig. l, the plate-iilament circuit of tube VT isjenergized from a source of fluctuating potential S, such as a rectifier,

CAD

filter condenser FC in a well known manner.

The low potential terminal of the source S is connected to the center tap CT through the primary A131 of an iron core transformer AT1 having a high step-up ratio, and through a biasing resistance BR series related. The high potential terminal of the source S is connected to the plate of the tube VT through the primary RP;x of the transformer RTB.

I have provided a connection between the grid of tube VT through the secondary Iii-S1 and the secondary AS1 to the low potential terminal of the bias resistor BR.

In Fig. 2, l have shown the modification of the system in that the low potential terminal of the source S is connected through the secondary ASQ of the high step-up ratio iron core transformer AT1 to the center tap CT, and have included the primary AP1 in the connection between the high potential terminal of the source S and the primary BP2. I have connected the grid of the tube VT through the secondary R51 to the low potential terminal of the source 53, the potential drop across the resistance of the secondary AS1 serving to maintain the average potential of the grid of tube VT negative with respect to its filament.

In each of the systems I have by-passed the radio frequency currents in the grid and plate circuits around the energizing system by means of radio frequency by-pass condensers C1 and C1 respectively.

Tn each of the systems the windings of the transformers AT1 and AT1 are so selected in ratio and so poled that the plate current of the tube VT is rendered devoid of any fluctuation in current due to the fluctuating potential energization thereof, so that the carrier currents are transferred from the primary HP1 to the resonant secondary RSZ in amplified form without being` modulated at .hum frequencies. i i

lt will be noted that inY the foregoing description I have limited my description to radio frequency stages, this because such a struct-ure, if applied to audio frequency stages would proiluce deregicno'ation of the audio `requency signal currents throush the tion of the transformers AT1 and 'ii-LT1 upon the .arid circuit of the tube VT.

It will be understood that minor detail changes may be made in the systems de scribed herein without departing' from the spirit of my invention as defined in the appended claims.

Havingr thus described my invention l claim 1. In a radio frequency amplifyingy system, the combination of a vacuum tube havingr input and output circuit-s, a source of fiuctuatingunidirecti'onal current, connections for energizing' the plate and grid electrodes from said source, and within the grid-filament and plate-filament circuits of said tube for varying; the impedance of said tube in consonance with the fluctuations of said source whereby high frequency currents are amplified by Said tube without modulation thereof by said source, said means consisting of a transformer, the primary of which is series connected within the plate-filament circuit of said tube, and the secondary of which is series connected wit-hin thc gridfilament circuit of said tube the windings of said primary and secondary being relatively proportioned and poled to produce said tube impedance variation.

2. In a radio frequencqv amplifying system, the combination of a vacuum tube having input and output circuits, a source of fluctuating unidirectional current, connections for energizing the plate and grid electrodes from said source, means within the grid-filament and plateefilament circuits of said tube for varying the impedance of said tube in con sonance with the fluctuations of said source whereby high frequency currents are amplified by said tube without modulation thereof by said source, said means consisting of a transformer, the primary of which is series connected within the plate-filament circuit of said tube, and the secondary of which is series connected within the grid-filament circuit of said tube the windings of said primary and secondary being relatively proportioned and poled to produce said tube irnpedance variation, and means for luypassingT the radio frequency currents directly from said input and output circuits to the cathode of said tube.

3. In a radio frequency amplifying system, the combination of a vacuum tube having input and output circuits, a source of fluctr. ting' unidirectional current, connections for energizing the plate and grid electrodes from said source, and means within the grid-{ilament and plate-filament circuits of said tube for varying the impedance of said tube in consonance with the iuctuations of said source whereby high frequency currents are amplilied by said tube without modulation thereof by said source, said means consisting?, of a transformer. the primary of which is series connected within the plate-filament circuit of said tube. and the secondary of which is series connected within the grid-filament circuit of said tube the windings of said primary and secondary being rel ativelv proportioned a n d poled to produce said tube impedance variation, the potential developed across the secondary of said transformer determining): the average potential of the Io frid of said tube relative to the cathode thereof.

t. In a radio frequency amplifyin system, the combination of a vacuum tube having input and output circuits, a source of fluctuating unidirectional current, connections for energizing the plate and grid electrodes from said source, and means within the grid-filament and plate-filament circuits of said tube for varying the impedance of said tube in consonance with the fluctuations of said source` whereby high frequency currents are amplilied by said tube without modulation thereof by said source, said means consisting of a transformer, the primary of which is series connected within the plate-filament circuit of said tube, and the secondary of which is series connected within the grid-filament circuit of said tube, the secondary of said transformer also series related within the platelament circuit of said tube, whereby the average potential of grid of said tube is determined by the potential drop across said secondary and the windings of said primary and secondary being relatively proportioned and poled to produce said tube impedance variation.

5. In a radio frequency amplifying system, the combination of a vacuum tube having input and output circuits, a source of fluctuati ing unidirectional current, connections for energizing the plate and grid electrodes from said source, and means within the grid-filament and plate-filament circuits of said tube for varying the impedance of said tube in consonance with the iiuctuations of said source whereby high frequency currents are amplified by said tube without modulation thereof by said source, said means consisting of a transformer, the primary of which is series connected within the plate-filament circuit of said tube, and the secondary of which is series connected within the gridfilament circuit of said tube, the secondary of said transformer also series related within the plate-filament circuit of said tube, whereby the average potential of grid of said tube is determined by the potential drop across said secondary and the windings of said primary and secondary being relatively proportioned and poled to produce said tube impedance variation, and means for shunting the radio frequency currents from said input and output circuits to the cathode of said tube around the primary and secondary of said transformer.

6. In a radio frequency amplifying system, the combination of a vacuum tube having input and output circuits, a source of fluctuating uni-directional current, connections for energizing1 the plate and grid electrodes from said source, and means within the grid-filament and plate-filament circuits of said tube for varying the impedance of said tube in consonance with the fluctuations of said source whereby high frequency currents are amplified by 'said tube without modulation thereof by said source, said means consisting of a transformer, the primary of which is series connected within the plate-filament circuit of said tube, and the secondary of which is series connected within the grid-filament circuit of said tube, the

windings of said primary and secondary being relatively proportioned and poled to produce said tube impedance variation, and a grid biasing resistor connected between the cathode of the tube and said seconda-ry.

7. In a radio frequency amplifying system, the combination of a vacuum tube having input and output circuits, a source of Vfluctuating uni-directional current, connections for energizing theplate and grid electrodes from said source, and means within the grid-filament and plate-filament circuits of said tube for varying the impedance of said tube in consonance with the fluctuations of said source whereby high frequency currents are amplified by said tube without modulation thereof by said source, said means consisting of a transformer, the primary of which is series connected within the platefilament circuit of said tube, and the second-A ary of which is series connected within'the grid-filament circuit of said tube, the windingsV of said primary and secondary being relatively proportioned and poled to produce said tube impedance variation, and means for by-passing the radio frequency currents directly from said input and output circuits to Vthe cathode of said tube, and a grid biasing resistor connected in series between the said secondary and the cathode of said tube.

8. In a radio frequency amplifying system, the combination of a vacuum tube having input and outputmcircuits, a source of fluctuating funi-directional current, connections for energizing the plate and grid electrodes from said source, and means within the grid-filament and plate-filament circuits of said tube for varying the impedance of said tube'in consonance with the fluctuations of said source whereby high frequency currents are amplified by said tube without modulation thereof by said source, said means consisting of a transformer, the primary of which is series connected within the platefilament circuit of said tube, and the secondary of which is series connected within the grid-filament circuit of said tu'be the windings ofsaid primary and secondary being relatively proportioned and poled to produce said tube impedance variation, the potential developed acrossthe secondary of said transformer determining the average potential of the grid of saidtube relative to the cathode thereof, and a radio frequency by-pass condenser connected across said primary and secondary.

In witness whereof, Ihave hereunto subscribed my name this 17th day of July, 1929.

BENJAMIN F. MIESSNER. 

